try to use the following format you had a typo and your date is probably NA
OTC$DATE=as.Date(OTC$DATE,ormat="%d/%m/%Y")
also please avoid using : aes(x=DATE,y=OTC$NotionalAmounts)
change to:
aes(x=DATE,y=NotionalAmounts)
your plot might be better with making the data long then facet:
please read the guidelines to make a reprex you can dput your data to make things easier for those who want to help you
library(tidyverse)
library(lubridate)
#>
#> Attaching package: 'lubridate'
#> The following objects are masked from 'package:base':
#>
#> date, intersect, setdiff, union
library(ggplot2)
OTC <- structure(list(DATE = structure(c(10407, 10591, 10772, 10956,
11138, 11322, 11503, 11687), class = "Date"),
NotionalAmounts = c(72106521.77,80276622.05, 81420274.61,
88156431.71, 93959822.42, 95150854.68,
99648589.78, 111058769.9),
GrossCreditExposure = c(1202805L,
1328580L, 1119372L, 1023011L,
936961L, 1080349L, 1019132L, 1170902L),
GrossMarketValues = c(2562152.803, 3209463.957, 2609693.198,
2793954.52, 2554920.528, 3161552.443, 3041485.503, 3783434.112)
),
row.names = c(NA, -8L), class = "data.frame")
#OTC$DATE <- as.Date(OTC$DATE,format="%d/%m/%Y")
OTC %>%
gather(key,value,-DATE) %>%
ggplot(data=.,
aes(x=DATE,
y=value))+
facet_wrap(key ~ .,scales="free_y", ncol=1, strip.position = "top") +
geom_line(aes(x = DATE, y = value,
color = key),
alpha = 0.6, size = 1)+
scale_y_continuous(labels = scales::label_dollar())

Created on 2021-04-29 by the reprex package (v2.0.0)