Short Answer 
To resolve message delivery issues, first verify the recipient’s phone number for accuracy. Next, advise the recipient to check with their carrier about any message blocking settings. If problems persist, consider using alternative messaging platforms like email or social media to maintain communication.
Step 1: Verify the Phone Number
Before taking further actions, ensure you have entered the correct phone number of the recipient. A small typo can prevent messages from delivering successfully. Double-check each digit and confirm with the recipient, if necessary. Accuracy in contact details can eliminate simple errors that lead to message blocking.
Step 2: Inquire About Message Blocking Settings
Ask the recipient to check with their phone carrier regarding their message blocking settings. They should contact customer support to see if message blocking is active on their account. If so, they can request to disable this feature, which will allow them to receive messages without any issues.
Step 3: Use Alternative Messaging Platforms
If the issue persists despite verifying the number and checking with the carrier, consider switching to an alternative messaging platform. Options include using email or social media messaging apps to communicate with the recipient. This allows for continued communication while the message blocking issue is being resolved.