How can I file other documents with the EPO as ISA, subsequent to the application?

You can submit subsequently filed documents (SFDs) to the EPO as ISA (e.g. rectification of obvious mistakes in the description, claims or drawings under Rule 91 PCT) via the EPO's Online Filing 2.0, by post or, in case of unavailability of Online Filing 2.0, using the EPO’s Contingency Upload Service (CUS).

Alternatively, you may use WIPO's ePCT service to file SFDs or a PCT Chapter II demand. The ePCT service can also be used for indicating the payment of fees related to the demand (see OJ EPO 2016, A78).