The system needs 7 bytes that are not regular expression fields. The [a-zA-Z0-9] text is an expression, so it is not valid. You would need something like: blahbla[a-zA-Z0-9][a-zA-Z0-9]... From the custom objects (data patterns) page, even though you're creating an app the same requirements apply: https://www.paloaltonetworks.com/documentation/71/pan-os/web-interface-help/objects/objects-custom-objects-data-patterns: Syntax for Data Patterns When adding a new pattern (regular expression), the following general requirements apply: The pattern must have string of at least 7 bytes to match. It can contain more than 7 bytes, but not fewer. The string match may or may not be case-sensitive, depending on which decoder is being used. When case-sensitivity is required, you would need to define patterns for all of the possible strings in order to match all variations of a term. For example, if you wanted to match any documents designated as confidential, you would need to create a pattern for “confidential”, “Confidential”, and “CONFIDENTIAL”.
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