When trying to create a new Network Object from Configuration > Objects > Network, the following error may appear if the Subnet Mask does not work with the Provided IP Address/Range:
Error: Network object IP address must be an IPv4 or IPv6 prefix format, e.g., '188.8.131.52/24'
The IP Network Address section of the page has been filled out with an IP Address/Range which does not fit into the Mask Length specific Subnet Mask length. For example, 192.168.0.37 refers to a specific host IP Address, but the Mask Length is set as /24. Since the mask used is meant to specify a whole IP Range, it will cause the error as mentioned above. The correct Subnet Mask to use would be /32 since that would specify only a single IP Address rather than a whole range.
Inspect the values entered and ensure that the Mask Length suits the IP Address/Range.