You need a visa for Papua New Guinea if you have a Solomon Islands passport
Visa options for Papua New Guinea
Visa on arrival for a maximum of 60 days
Travelers need a visa to visit Papua New Guinea for Business or Tourism. Travelers can get a visa on arrival in Papua New Guinea at the port of entry, such as an international airport or border crossing. Travelers must show proof of a return ticket. Travelers can get a visa on arrival at Jackson’s International Airport in Papua New Guinea.
This is not offered by sherpa°.
Apply on the government site.