Do I need to pay on repurchasing Procreate for my iPad?

Re: If i buy pro create on my iphone, and i want to download it on another device (ipad) do i have to pay for it again?

If you don't receive the answer you seek in the Apple Community

You might want to ask the developers:

https://help.procreate.com/support

or

If intending to buy from the App Store:

You could use the "Get Support" link at the bottom of their web-page

Subscriptions and Billing - Official Apple Support

If they are both signed into the same account then typically you can download it to both of your devices provided there is an iPad version for the app. In fact according to https://apps.apple.com/us/app/procreate/id425073498 there is only an iPad version. Are we referring to the same app? I see there is also https://apps.apple.com/us/app/procreate-pocket/id916366645 which is listed as a different app under a different name (which you did not ask about!) In that case you probably have to pay for them individually.