Happens to me as well. Fastlane is up to date (version 2.4.0), using official plugin (https://github.com/getsentry/fastlane-plugin-sentry).
[03:13:41]: Will upload dSYM(s) to https://app.getsentry.com/api/0/projects/xxx/xxx/files/dsyms/
[03:13:41]: Uploading... /xxx.dSYM.zip
[03:14:46]: Error: 413 Request Entity Too Large
Organization and project slugs are ok, as well as auth token, because when we repeat the upload with the same dsym file sometimes it works. Uploaded dsym size is 25MB.
There's nothing to wonder at, error "413 Request Entity Too Large" is triggered by nginx when uploaded file size is greater than nginx's "client_max_body_size" setting. It seems that some of your nginx instances is improperly configured.
Looks like this error has happened before:
We are paying for this service, it's really great, but we have 4 projects depending on this functionality and currently it breaks our continuous deployment process.