regular expression in a variable, how to handle special characters?

Question

I'm trying to make API calls to Google Analytics and need to send regular expression as part of call using googleAnalyticsR package.

regular expression can be sent because I have special charaacter() in it. using double \ make it wrong when sent to API.

library(googleAnalyticsR)
date_range = c("2019-03-01", "2019-03-10")
view_id = "12345678"
reg_exp <- "(www.abc.com)\.*"
se <- segment_element("pagePath",
                  operator = "REGEXP",
                  type = "DIMENSION",
                  expressions = reg_exp,
                  scope = "SESSION")
sv_simple <- segment_vector_simple(list(list(se)))
seg_defined_one <- segment_define(sv_simple)
segment4 <- segment_ga4("simple", user_segment = seg_defined_one)

data <- google_analytics(view_id, 
               date_range = date_range,
               metrics = c("pageviews", ""),
               dimensions = c("pagePath"),
               segments = segment4)

How can I set the correct regexp in that variable?