You should carefully read the instructions and make sure you did verything right, you have the right versions ... I don't know the plugin but sinatures, i guess you have to set some up first. Did you?
If you sure there is a problem then you should go to the github page for all his repositorys look for the signature plugin and then report an issue.
You should also give this guy some stars he have deved a huge amount of plugins.
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April 20, 2021: Q2A 1.8.6 released!