i create a website where a user have to full out a form. After that the form starts to call an api with this input. Unfortunately the api is very slow. somtimes the user have to wait one minute.

I read if the user have to wait so long it is better to use a progress bar instead of a spinner http://uxmovement.com/navigation/progress-bars-vs-spinners-when-to-use-which/

I can not predict how long the api call will last. Therefore, an accurate display of the progress is difficult.

Do you have experiences or ideas to handle this?