"We need to pay for these sausages."
Translation:Tenemos que pagar estos chorizos.
Perhaps Duo wants us to learn that tener que is also used as we often use "to need to" (even though using "to need to" may not be strictly correct, according to lulularosa's and GypsyMaggie's standards). For example, I can easily imagine saying "Just a minute, I need to pay for these xxxxs" to my husband standing at the end of a check-out line saying "Let's go!" Un momento, tengo que pagar . . . . would be appropriate in Spanish, I think.
While I was reading these comments I had to think of conversations with my boss, a long time ago. He might say, "you need to pay more attention." But in some cases it was, "You have to pay more attention." When the situation was really serious he would say, "You want to pay more attention" - the implication being "if you want to keep your job."
So, to me it's all a matter of degrees, and who is saying it to whom.
Using "need to" and "have to" interchangeably is usually a bit of lazy thinking that most of us fall into from time to time. "need to" , in most circumstances, implies an interior impetus, while "have to" some external requirement. See, for instance, GypsieMaggie's comment below.