Hi! Indeed, that seems to be the issue here. After running the code below (developed by Claude Code) I was able to overcome that error (I got a new one, but in this case, it is something that is on my end to fix because it's related to package versions). I will leave the code below in case is helpful in any way 
# Workaround for a bug in rsconnect 1.11.0 (current CRAN release as of
# 2026-08-25; still unfixed/unreported upstream as of this writing) that
# breaks deploying/re-deploying to Posit Connect Cloud whenever the
# deployment has no `envVars` configured:
#
# Error in mapply(FUN = f, ..., SIMPLIFY = FALSE) :
# zero-length inputs cannot be mixed with those of non-zero length
#
# Root cause
# ----------
# rsconnect:::connectCloudClient()'s createContent() and updateContent()
# closures build the "secrets" payload sent to Connect Cloud like this:
#
# secrets <- unname(Map(function(name, value) list(name = name, value = value),
# envVars, Sys.getenv(envVars)))
#
# When `envVars` is NULL/character(0) (i.e. no envVars configured for the
# app -- true for any fresh deploy/migration that never passed `envVars =`
# to deployApp()), `Sys.getenv(NULL)` does NOT return character(0). It
# treats a NULL/empty filter as "no filter" and returns *every*
# environment variable in the R session instead. Map()/mapply() then gets
# one zero-length argument and one 70+-length argument mixed together,
# which errors out with the message above.
#
# Fix
# ---
# Redefine connectCloudClient() in the rsconnect namespace (for this R
# session only -- nothing is written to disk or to the installed package)
# so both call sites route through a small helper that short-circuits to
# character(0) when envVars is empty, instead of falling through to the
# buggy Sys.getenv(NULL) behavior.
#
# Usage: source this file once, before calling rsconnect::deployApp() /
# rsconnect::deploySite() for a Posit Connect Cloud target. See
# dev/03_deploy.R.
patch_rsconnect_envvars_bug <- function() {
if (!requireNamespace("rsconnect", quietly = TRUE)) {
stop("rsconnect is not installed.")
}
ns <- asNamespace("rsconnect")
orig <- get("connectCloudClient", envir = ns)
body_txt <- paste(deparse(body(orig)), collapse = "\n")
marker <- "rsconnectEnvVarsPatch_safeGetenv(envVars)"
n_marker <- length(gregexpr(marker, body_txt, fixed = TRUE)[[1]])
if (n_marker == 1 && gregexpr(marker, body_txt, fixed = TRUE)[[1]][1] == -1L) {
n_marker <- 0
}
if (n_marker == 2) {
# Already patched earlier in this session (e.g. this file was
# source()d more than once) -- nothing to do.
message(
"[patch] rsconnect::connectCloudClient() already patched for ",
"this session; skipping."
)
return(invisible(TRUE))
}
target <- "Sys.getenv(envVars)"
n <- length(gregexpr(target, body_txt, fixed = TRUE)[[1]])
if (n == 1 && gregexpr(target, body_txt, fixed = TRUE)[[1]][1] == -1L) {
n <- 0
}
if (n != 2) {
stop(
"patch_rsconnect_envvars_bug(): expected to find 2 occurrences ",
"of `Sys.getenv(envVars)` inside rsconnect:::connectCloudClient() ",
"(one in createContent(), one in updateContent()), but found ", n,
". The installed rsconnect internals may have changed since this ",
"patch was written (installed version: ",
as.character(utils::packageVersion("rsconnect")), "). ",
"Skipping the patch rather than risk silently breaking deployment -- ",
"check https://github.com/rstudio/rsconnect for a real fix first."
)
}
patched_body_txt <- gsub(
target,
"rsconnectEnvVarsPatch_safeGetenv(envVars)",
body_txt,
fixed = TRUE
)
new_body <- parse(text = patched_body_txt)[[1]]
patched <- orig
body(patched) <- new_body
patch_env <- new.env(parent = environment(orig))
patch_env$rsconnectEnvVarsPatch_safeGetenv <- function(x) {
if (length(x) == 0) character(0) else Sys.getenv(x)
}
environment(patched) <- patch_env
assignInNamespace("connectCloudClient", patched, ns = ns)
message(
"[patch] rsconnect::connectCloudClient() patched for this session ",
"to fix the 'zero-length inputs cannot be mixed' bug when envVars ",
"is empty (see dev/patch_rsconnect_envvars_bug.R)."
)
invisible(TRUE)
}
patch_rsconnect_envvars_bug()
