I don’t use the solcast card.
When you check your credentials, make sure that you are entering the correct values from your logon in the Solcast site.
The resource ID should be obvious but the API key is hidden away.
To reveal it, select the down arrow, top right.
You can then select and copy your API key.
I can see my Solcast sites on the Solcast app. I use predbat and the Solcast predictions are coming through correctly.
bear in mind that there is a limit of 10 API calls to solcast a day, and if you have two sites (arrays/orientations) then each counts as 1 API call, so really only 5 a day
its possible you have exhausted the API calls because every time you refresh the solcast card it makes another call