We get a lot of my XXX is not charging, it does YYY but lights ZZZ.
This is what to do:
the most common to fail physical part is the cable, it can have failures at any part of it's length. This usually manifests as slow charging as a trickle gets through into or out of the portable charger. Try different cable(s).
try different charger. Are you using a charger as powerful as the portable charger needs? A typical need is for 2A but some benefit from 2.4A, or dual inputs, or QC input.
are your expectations valid? It might be behaving exactly as it should. Go to the product page on anker.com and look for charging time, it is usually in the description section, or in FAQ lower down or in the linked Amazon page description or it's questions section.
After all of that then you can attempt to get an answer here, but the above is pretty much our stock help, so then email
Include your order details (e.g. Amazon order), serial number off the packaging or on a cable, with a description of the issue and evidence you tried all the above, then support will quickly help.