"allows to" requires a subject (e.g. "allows one to"), without it's just
syntactically wrong. Change the verb entirely to workaround the
problem.
[\fBargument\fR [\fBargument\fR]]
.IR ...
.SH DESCRIPTION
-A client for ACME-based Certificate Authorities, such as LetsEncrypt. It
-allows to request and obtain TLS certificates from an ACME-based
+A client for ACME-based Certificate Authorities, such as LetsEncrypt. It can
+be used to request and obtain TLS certificates from an ACME-based
certificate authority.
Before any certificates can be requested, Dehydrated needs