How to pay voluntary pension in Portugal ?!

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If I am not currently employed, can I make voluntary pension contributions in Portugal? I solely receive income from dividends and earnings generated in other countries, and taxed there with that "withhold tax". If necessary I am considering create a "sole propiertership" "business in my own name" and working for a short period of time in order to be eligible for a pension in Portugal and to have access to health insurance in case of emergencies. I have observed that individuals who work only need to work for three months each year to receive credit for a full year of work in Portugal national pension plan. Can I establish a sole proprietorship and work for only three months each year, providing programming services to some acquaintances or old clients for example ? I have more than sufficient funds from cryptocurrency investments and dividends, and I no longer wish to work as I can comfortably live on 2-3k/month. In fact, I could personally manage with just $5 per day for my food expenses. I do not have any dependents, such as children or a spouse, and I am the owner of the residence I currently reside in,so i also live rent free.