“On my table there are many invitation letters from far away in the country? What can I do to work for them? I am well known, widely all around Tanzania. This is my problem for which I need your explanation.”
I know there are a lot of needs in Africa, and very limited resources. It takes money to travel and meet with the brethren in distant places. Hopefully the brethren who have asked you to come are willing to help a little with the expenses of your trip, and your needs while there, just as Jesus expressed in Luke 10:4, 7. However, all the brethren who need a visit may not be able to help you with your expenses, and therefore you need to get help elsewhere. Paul wrote to the Corinthians, “I robbed other churches, taking wages of them, to do you service.” (2 Corinthians 11:8) The excess of other churches served to supply the lack in those who were more needy. This is something that needs to be done a lot in Africa because of the widespread poverty there. It is the responsibility of every Christian in richer countries to financially help ministers in poorer countries to spread the gospel. (I know of many ministers struggling to preach the true gospel in Africa who are receiving little or no support from overseas.) Even if help comes from overseas, the brethren there should help as much as they can, and then pray that the Lord will provide what is lacking.
In addition to you making visits, you should heed the counsel of Paul to Timothy. He wrote, “And the things that thou hast heard of me among many witnesses, the same commit thou to faithful men, who shall be able to teach others also.” (2 Timothy 2:2) When Jesus was here He trained twelve disciples to spread the gospel. They, in turn, trained others to do the same thing, and today the message has reached most of the world. This same process needs to be repeated over and over until “this gospel of the kingdom shall be preached in all the world for a witness unto all nations.” (Matthew 24:14)
I hope this helps to answer your question.