Postgres GIN index on (VARCHAR, JSONB)
Two indexes

Simply create two separate indexes. PostgreSQL will use both where appropriate.

CREATE INDEX ON table1 (account);
CREATE INDEX ON table1 USING GIN (json);


Using an extension

Or you can use the btree_gin.


  btree_gin provides sample GIN operator classes that implement B-tree equivalent behavior for the data types int2, int4, int8, float4, float8, timestamp with time zone, timestamp without time zone, time with time zone, time without time zone, date, interval, oid, money, "char", varchar, text, bytea, bit, varbit, macaddr, inet, and cidr.


It looks like this,

CREATE EXTENSION btree_gin;
CREATE INDEX ON table1 USING gin (account,json);


Under normal circumstances, I'd likely use two indexes.