Hello,

I have attached a screenshot please check. Click Here

After create subscription  copy the product i'd and go to your Admin panel and Put your Price and Product I'd inside your IAP Subscription Page
And make sure you have added your Product I'd Correctly and Same Product I'd that you have created.

Plan I'd and Base Plan I'd will be Same, Mean create 1 Plan > Put I'd after that Create Base Plan  using same I'd Inside that and Select  (auto-renewing) then Put Your Price.

Thanks..