You are only posting the error. Please add the full logs for the request. Example:
DEBU[0015] API: New request /rest/updatePlaylist client=NavidromeUI requestId=Mac.lan/7TOEL9X6di-000002 username=admin version=1.8.0
TRAC[0015] SQL: `SELECT * FROM user WHERE user_name = {:p0} COLLATE NOCASE` args="map[p0:admin]" elapsedTime="853.666µs" requestId=Mac.lan/7TOEL9X6di-000002 rowsAffected=1
TRAC[0015] SQL: `UPDATE user SET last_access_at = {:p0} WHERE id = {:p1}` args="map[p0:2025-02-15 16:17:20.46454 -0500 EST m=+15.704714335 p1:6f9786e8-3b84-4d9d-865e-1f8dda2682a5]" elapsedTime="527.417µs" requestId=Mac.lan/7TOEL9X6di-000002 rowsAffected=1
TRAC[0015] Update user's lastAccessAt elapsed=2.2ms requestId=Mac.lan/7TOEL9X6di-000002 username=admin
TRAC[0015] playerId found in cookies playerId=aba5499a-0748-49cf-9bae-b49fc941587d requestId=Mac.lan/7TOEL9X6di-000002
TRAC[0015] SQL: `SELECT player.*, user.user_name username FROM player JOIN user ON player.user_id = user.id WHERE player.id = {:p0}` args="map[p0:aba5499a-0748-49cf-9bae-b49fc941587d]" elapsedTime="981.041µs" requestId=Mac.lan/7TOEL9X6di-000002 rowsAffected=1
TRAC[0015] SQL: `UPDATE player SET client = {:p0}, id = {:p1}, ip = {:p2}, last_seen = {:p3}, max_bit_rate = {:p4}, name = {:p5}, report_real_path = {:p6}, scrobble_enabled = {:p7}, transcoding_id = {:p8}, user_agent = {:p9}, user_id = {:p10} WHERE id = {:p11}` args="map[p0:NavidromeUI p1:aba5499a-0748-49cf-9bae-b49fc941587d p10:6f9786e8-3b84-4d9d-865e-1f8dda2682a5 p11:aba5499a-0748-49cf-9bae-b49fc941587d p2:127.0.0.1 p3:2025-02-15T16:17:20.472275-05:00 p4:0 p5:NavidromeUI [IntelliJ HTTP Client] p6:false p7:true p8: p9:IntelliJ HTTP Client]" elapsedTime="531.083µs" requestId=Mac.lan/7TOEL9X6di-000002 rowsAffected=1
DEBU[0015] Updating playlist id=30b3d166-0c26-42b7-bbe2-681fbbda04d2 requestId=Mac.lan/7TOEL9X6di-000002
TRAC[0015] -- Adding: '[]' requestId=Mac.lan/7TOEL9X6di-000002
TRAC[0015] -- Removing: '[0]' requestId=Mac.lan/7TOEL9X6di-000002
TRAC[0015] SQL: `SELECT playlist.*, user.user_name as owner_name FROM playlist JOIN user on user.id = owner_id WHERE (playlist.id = {:p0} AND (1=1))` args="map[p0:30b3d166-0c26-42b7-bbe2-681fbbda04d2]" elapsedTime="699.792µs" requestId=Mac.lan/7TOEL9X6di-000002 rowsAffected=1
TRAC[0015] SQL: `SELECT playlist.*, user.user_name as owner_name FROM playlist JOIN user on user.id = owner_id WHERE (playlist.id = {:p0} AND (1=1))` args="map[p0:30b3d166-0c26-42b7-bbe2-681fbbda04d2]" elapsedTime="298.25µs" requestId=Mac.lan/7TOEL9X6di-000002 rowsAffected=1
TRAC[0015] SQL: `SELECT coalesce(starred, 0) as starred, starred_at, coalesce(play_count, 0) as play_count, play_date, coalesce(rating, 0) as rating, f.*, playlist_tracks.* FROM playlist_tracks LEFT JOIN annotation on (annotation.item_id = media_file_id AND annotation.item_type = 'media_file' AND annotation.user_id = '6f9786e8-3b84-4d9d-865e-1f8dda2682a5') JOIN media_file f on f.id = media_file_id WHERE playlist_id = {:p0} ORDER BY playlist_tracks.id` args="map[p0:30b3d166-0c26-42b7-bbe2-681fbbda04d2]" elapsedTime=7.2ms requestId=Mac.lan/7TOEL9X6di-000002 rowsAffected=31
TRAC[0015] SQL: `SELECT count(*) as exist FROM playlist WHERE (id = {:p0} AND (1=1))` args="map[p0:30b3d166-0c26-42b7-bbe2-681fbbda04d2]" elapsedTime="155.875µs" requestId=Mac.lan/7TOEL9X6di-000002 rowsAffected=1
TRAC[0015] SQL: `UPDATE playlist SET comment = {:p0}, duration = {:p1}, evaluated_at = {:p2}, id = {:p3}, name = {:p4}, owner_id = {:p5}, path = {:p6}, public = {:p7}, size = {:p8}, song_count = {:p9}, sync = {:p10}, updated_at = {:p11} WHERE id = {:p12}` args="map[p0:Auto-imported from 'yussef.m3u' p1:7410.33 p10:true p11:2025-02-15T16:17:20.494073-05:00 p12:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p2:<nil> p3:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p4:yussef p5:6f9786e8-3b84-4d9d-865e-1f8dda2682a5 p6:/Users/deluan/Music/Picard/yussef.m3u p7:false p8:1070813888 p9:31]" elapsedTime="462.459µs" requestId=Mac.lan/7TOEL9X6di-000002 rowsAffected=1
TRAC[0015] SQL: `DELETE FROM playlist_tracks WHERE playlist_id = {:p0}` args="map[p0:30b3d166-0c26-42b7-bbe2-681fbbda04d2]" elapsedTime="92.208µs" requestId=Mac.lan/7TOEL9X6di-000002 rowsAffected=31
TRAC[0015] SQL: `INSERT INTO playlist_tracks (playlist_id,media_file_id,id) VALUES ({:p0},{:p1},{:p2}),({:p3},{:p4},{:p5}),({:p6},{:p7},{:p8}),({:p9},{:p10},{:p11}),({:p12},{:p13},{:p14}),({:p15},{:p16},{:p17}),({:p18},{:p19},{:p20}),({:p21},{:p22},{:p23}),({:p24},{:p25},{:p26}),({:p27},{:p28},{:p29}),({:p30},{:p31},{:p32}),({:p33},{:p34},{:p35}),({:p36},{:p37},{:p38}),({:p39},{:p40},{:p41}),({:p42},{:p43},{:p44}),({:p45},{:p46},{:p47}),({:p48},{:p49},{:p50}),({:p51},{:p52},{:p53}),({:p54},{:p55},{:p56}),({:p57},{:p58},{:p59}),({:p60},{:p61},{:p62}),({:p63},{:p64},{:p65}),({:p66},{:p67},{:p68}),({:p69},{:p70},{:p71}),({:p72},{:p73},{:p74}),({:p75},{:p76},{:p77}),({:p78},{:p79},{:p80}),({:p81},{:p82},{:p83}),({:p84},{:p85},{:p86}),({:p87},{:p88},{:p89})` args="map[p0:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p1:517cb6295429baa4123a97a217c973e1 p10:7b35b4acd3b2ead425765b92edd71013 p11:4 p12:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p13:0b7cf959a86e860d02066de75f6187c3 p14:5 p15:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p16:b8102798b50325ec4e040c49e4174538 p17:6 p18:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p19:7c9df4d9b053de14ae8ece57193ee035 p2:1 p20:7 p21:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p22:6f9a5149bdea3f8340ae306cf411d994 p23:8 p24:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p25:550472955d6c0b5280c068330fe6c294 p26:9 p27:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p28:053df360495b418fbde46693e22ff653 p29:10 p3:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p30:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p31:966ccc58ad50f2a50f35944f235d67f8 p32:11 p33:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p34:7fdc686997f95ee0580090a3c5ba37e5 p35:12 p36:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p37:11a225797f2990b04142c3c4dfc46abe p38:13 p39:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p4:0cec72db00eaeb2e6052b27c89bc025c p40:1aed50ec237d97cfdd53a219022ae4fe p41:14 p42:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p43:9c7cf72a7430ad6ecd5fe64339713b3c p44:15 p45:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p46:e177248c4ae82032f5d6a8c36f54ce63 p47:16 p48:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p49:7f8918dd5b39475b92a60a99de9351d9 p5:2 p50:17 p51:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p52:674d2382f722b161deba1bd33ab136da p53:18 p54:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p55:2bb62dd15368bfad501e779813e67428 p56:19 p57:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p58:5c2f5c7a1103ba15e6942fe4b5116f0b p59:20 p6:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p60:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p61:7649395d36b6d2a376c945ca6f9ea5fc p62:21 p63:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p64:5a081c2f89662321e799d9adf91a0a1d p65:22 p66:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p67:802d9d8829507c4522509a5f8aa209fb p68:23 p69:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p7:9f940731c4351ea65a1458d652b92082 p70:192366c25ae6a8946a1641f6c2be8a5a p71:24 p72:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p73:dc7bac3704729ea87ca4963272971f3d p74:25 p75:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p76:605030f56891f7ab211b2fe710f2e532 p77:26 p78:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p79:86333730b5c871161146aab89630c909 p8:3 p80:27 p81:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p82:59770d8f8c6b233e44591e600841b608 p83:28 p84:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p85:ac44fd741353a5e739dca182dec53404 p86:29 p87:30b3d166-0c26-42b7-bbe2-681fbbda04d2 p88:d36b1427daa1bbbba72aebfe6bb855f6 p89:30 p9:30b3d166-0c26-42b7-bbe2-681fbbda04d2]" elapsedTime="656.083µs" requestId=Mac.lan/7TOEL9X6di-000002 rowsAffected=30
TRAC[0015] SQL: `SELECT coalesce(sum(duration), 0) as duration, coalesce(sum(size), 0) as size, count(*) as count FROM media_file JOIN playlist_tracks f on f.media_file_id = media_file.id WHERE playlist_id = {:p0}` args="map[p0:30b3d166-0c26-42b7-bbe2-681fbbda04d2]" elapsedTime="287.583µs" requestId=Mac.lan/7TOEL9X6di-000002 rowsAffected=1
TRAC[0015] SQL: `UPDATE playlist SET duration = {:p0}, size = {:p1}, song_count = {:p2}, updated_at = {:p3} WHERE id = {:p4}` args="map[p0:7213.89 p1:1.0340683e+09 p2:30 p3:2025-02-15 16:17:20.510207 -0500 EST m=+15.750381293 p4:30b3d166-0c26-42b7-bbe2-681fbbda04d2]" elapsedTime="136.125µs" requestId=Mac.lan/7TOEL9X6di-000002 rowsAffected=1
DEBU[0015] API: Successful response body="{\"subsonic-response\":{\"status\":\"ok\",\"version\":\"1.16.1\",\"type\":\"navidrome\",\"serverVersion\":\"dev\",\"openSubsonic\":true}}" endpoint=/rest/updatePlaylist requestId=Mac.lan/7TOEL9X6di-000002 status=OK
DEBU[0015] HTTP: POST http://localhost:4533/rest/updatePlaylist?u=admin&p=[REDACTED]&f=json&v=1.8.0&c=NavidromeUI elapsedTime=56.2ms header="{\"Accept\":[\"*/*\"],\"Accept-Encoding\":[\"br, deflate, gzip, x-gzip\"],\"Content-Length\":[\"67\"],\"Content-Type\":[\"application/x-www-form-urlencoded\"],\"Cookie\":[\"nd-player-61646d696e=aba5499a-0748-49cf-9bae-b49fc941587d\"],\"User-Agent\":[\"IntelliJ HTTP Client/IntelliJ IDEA 2024.3.2.2\"]}" httpStatus=200 remoteAddr="127.0.0.1:51465" requestId=Mac.lan/7TOEL9X6di-000002 responseSize=117
It starts with API: New request /rest/updatePlaylist
and ends with HTTP: POST http://localhost:4533/rest/updatePlaylist
EDIT: What we are looking for is the HTTP: POST http://localhost:4533/rest/updatePlaylist
line, that shows the request headers