Category:Articles with invalid ISSNs

This is a maintenance category for articles with invalid ISSNs. It is sometimes added by the template, which should be located next to the ISSN with the problem. Articles can also be included in this category if an ISSN used in an ISSN or ISSN link template is not valid. The most likely reason is a bad checksum, (see ISSN) which probably means there is a typing error in the ISSN. Also, ISSNs that are not eight digits in a 4-4 pattern (i.e.: ISSN 1234-5678) will return an error message. Use an upper-case "X", not a lower-case "x", if "X" is the final character in the ISSN. The two groups of four characters are joined with a hyphen, not a dash. See also Category:CS1 errors: ISSN