It seems like CORS (Cross-Origin Resource Sharing) is not properly setup or your Cloud Run can’t handle the POST method.

Found this answer by John Hanley from this post that might be helpful for you:

Notice the HTTP 302 response on your POST. That means the client is being instructed to go to a new Location. Your client is then converting the POST into a GET and making another request at the new location.

Cloud Run only supports HTTPS. Your POST request is being sent to an HTTP endpoint. The Cloud Run frontend will automatically redirect the client to the HTTPS endpoint.

Change your request from using HTTP to HTTPS.

You can also check this documentation about Handling CORs (a way to let applications running on one domain access another domain) and CORS limitations since you are encountering a CORS Error.