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That would be owing either to having an inadequate ribbon (worn out), or having a ribbon that is not seated properly against the turning wheel so that the ribbon does not advance (and gets worn out typing against just one spot on the ribbon, which you can examine to look for a telltale sign of this: one worn spot right under the point where the hammer strikes the ribbon by way of the daisywheel), or else the mechanism for that turning wheel is not actually turning, or else the hammer is adjusted too far away or 'too weak' and doesn't strike hard enough, or the hammer itself is defective or too weak despite adjustment.
So check the ribbon, check whether it has one worn-out spot on it, make sure it is seated properly, and adjust the hammer strength or closeness to maximum. After that, your typewriter may need varying kinds of repair, depending upon what is observed. Let me know what you see and what you find out... and if you need a manual for your model, let me know that too.