Can you try this as a formula Rich Text button (ie not a formula URL) and let me know if it works in Edit Mode? I think it will also work in view mode (but not Add Mode).
var text URL = URLRoot() & "db/" & Dbid() & "?a=API_EditRecord" & "&apptoken=MyAppToken"
& "&rid=" & URLEncode([Record ID#]) & "&_fid_921=1" & "&rdr="&URLEncode(URLRoot() & "db/" & Dbid() & "?a=er&dfid=34&rid=" & ToText([Record ID#]) & "&page=16");
"<a class='SaveBeforeNavigating' data-replaceRid=true style=\"text-decoration:none; background: #1ba802; border-radius: 5px; color: #ffffff; display: inline-block; padding: 0px 0px 0px 0px; width:100px; text-align: center; text-shadow: none; border: 2px solid #1ba802; font-size: 12px \"href='"
& $URL
& "'>Submit</a>"