Hey there @Imee19 --- let's start over. The error message you reported above appears to be the exact same error message discussed on the DADA2 issue tracker. The issue on the DADA2 issue tracker mentions that one way that this error crops up is when all the reads in the input are unique --- the error model has nothing to work with, since there are no repeated reads. It is possible that you have run into this situation. Reading more of the issue tracker, one possible solution is to proceed with only your forward reads.
Outside of DADA2 - other options to try are OTU clustering or deblur. Hope that helps! 