Hello,
Whether the AP version is the same as the AC version. Is the AP a fat AP or a fit AP?
Possible Causes of AP Online Failure:
The AP is not assigned an IP address, or the static IP address of the AP is incorrectly configured.
The network between the AP and AC is disconnected due to incorrect configurations.
The AP fails MAC address or SN authentication.
The license resources are insufficient, and the maximum number of APs that can be connected to the AC is limited.
The MAC address, SN, and type configured for the AP are not consistent with the actual ones.
Kindly refer to the following guide for troubleshooting:
AP Online Failure