Due to certain issues on Facebook's side, referral links may not work correctly on iOS devices currently, which mainly affects Messenger Ref URL Growth Tool in ManyChat. QR Code Growth Tool, SMS and Email messages with referral links in them can also be affected.
You may notice messages not being triggered at all after clicking referral links, or a conversation with the page in Messenger displayed incorrectly showing unidentified Facebook User.
You can track this issue's status in the following bug thread on Facebook: https://developers.facebook.com/support/bugs/679578949452438/
More information to follow.