You need an ETA for Cape Verde if you have a Guinean passport
Visa options for Cape Verde
Electronic travel authorization
Travellers need travel authorization to visit Cape Verde for Business or Tourism. The Electronic Travel Authorization (EASE) for Cape Verde is required for visa-exempt visitors entering Cape Verde. It is an online application. If approved, travellers will receive an eTA confirmation electronically. When travellers arrive in Cape Verde, the border crossing will ask for a passport and check electronic records to ensure travellers have the proper visa. Travellers should complete the EASE application online a minimum of 5 days before travelling to Cape Verde.
This is not offered by sherpa°.
Apply on the government site.