mailer error: NoMethodError: undefined method `keys' for #<String:0x00005596d86d0708

[crackfoo]

I'm using:

peatio: 2.6.29
barong: 2.6.31

And seeing these errors in the mailer log:

mailer_1                | {"level":"ERROR","time":"2021-02-25 18:21:36 +0000","message":"#<NoMethodError: undefined method `keys' for #<String:0x00005596d86d0708>>"}
mailer_1                | {"level":"ERROR","time":"2021-02-25 18:21:38 +0000","message":"#<NoMethodError: undefined method `keys' for #<String:0x00005596d86d0460>>"}

Any hints on what is the cause?

[crackfoo]

as well, the mailer constantly reports:

mailer_1                | {"level":"ERROR","time":"2021-03-16 13:08:44 +0000","message":"#<NoMethodError: undefined method `keys' for \"changes.state == \\\"submitted\\\" && record.state == \\\"accepted\\\"\":String>"}
mailer_1                | {"level":"ERROR","time":"2021-03-16 13:10:11 +0000","message":"#<JWT::ExpiredSignature: Signature has expired>"}