Rae from Shopify here. Thank you for reaching out about this. I'm happy to help out!
As a starting point, can you please confirm that you've set up the Facebook channel entirely by following these steps? Then, did you also set up Instagram Shopping completely by following these steps?
If so, there are a few extra troubleshooting steps we can try out to make sure your accounts are set up correctly. Firstly, please log in to your Facebook Commerce Manager account directly on Facebook, and under 'Business Manager > Settings > Business Assets', ensure your business Instagram account is set to 'Visible'.
Next, please visit your Facebook business page directly on Facebook's end. From here, click 'Settings > Instagram' and make sure your business Instagram account - not your personal Instagram account - is linked here.
Then, open up the Instagram app on your mobile device, head to your business page profile, and click 'Edit profile > Page' to double check that your Facebook business page is linked to your Instagram account correctly.
Please keep me posted on how this goes, and if you're still noticing a blank screen on your end after completing the above steps. I look forward to hearing back from you soon!