When using the pq library along with pgbouncer, the following error is generated:
Pooler Error: Unsupported startup parameter: extra_float_digits

As a workaround, one could follow the instructions in Athou/commafeed#559

However, better control over the sent configuration would be a better approach.

i.e. existing library is hard-coding the following :
o.Set("extra_float_digits", "2")

which is the suspected cause for the issue.