Hello there User123-,
Thanks for posting here on the Apple Support Communities! This is a place where other Apple users can submit questions or respond to others to help lend a hand.
We understand you’re having some issues downloading pictures from Messages. Let's take a closer look as we do our best to provide some additional insight.
To get started, does this keep happening after a restart or are there any updates available for your device?
How to back up your iPhone, iPad, and iPod touch
Update your iPhone, iPad, or iPod touch
If so, are there any changes after giving that a try? Also, since this would require having enough storage space on your iPhone, how much storage space is available on your iPhone? How to check the storage on your iPhone, iPad, and iPod touch Keep in mind that this is different from iCloud Storage.
We hope this helps get you pointed in the right direction.
Take care.